The invention is in an aqueous bath which contains tetrammine palladium dibromide, ammonium bromide and ammonium hydroxide and is useful in the galvanic depositing of palladium coatings.
In Transactions of the Institute of Metal Finishing, 1968, Vol. 46, pp. 26 to 31, a description is given of the galvanic depositing of palladium from aqueous solutions containing tetrammine palladium dibromide, ammonium bromide and ammonium hydroxide. The palladium coatings obtained are ductile and have a dull sheen.
German Pat. No. 1,262,722 discloses a bath consisting of an aqueous alkaline-ammoniacal solution of tetrammine palladium dibromide for the galvanic depositing of palladium coatings on electrical contacts.
The bath described in German Offenlegungschrift No. 3,045,968 for the galvanic production of palladium coatings contains diammine palladium dichloride and/or diammine palladium dibromide, sulfamic acid and ammonium chloride, and has a pH of about 6.5 to 10. The coatings are ductile and generally not porous; thinner coatings may be porous.
U.S. Pat. No. 3,458,409 discloses a method of depositing bright palladium from aqueous ammoniacal palladium salt solutions (pH&gt;9.5) containing pyridine, pyridine carboxylic acid or pyridine carboxylic acid amides as bright-finishing agents. To obtain bright palladium coatings of greater thickness, (more than 5 micrometers), the lead salt of ethylene diamine tetracetic acid is added to the bath. Diammine palladium dichloride is named as a palladium salt that is especially suitable for this process.
The problem presented was to find a bath for the galvanic depositing of palladium coatings which would provide firmly adherent, ductile coatings on nickel, nickel alloys, nonferrous metals and their alloys, and which would be not only free of pores and fissures but also bright, with low internal stresses.